This invention relates to retainers for cable connectors which mount through an aperture in a metal chassis of electrical or electronic equipment. The invention is more particularly concerned with a combined retainer and grounding terminator for grounding to the chassis the braids or ground conductors of signal conductors or cables within the equipment which are coupled to the associated connector.
Over the years, a variety of techniques have been employed for terminating electrical components where the wire braids or shields are terminated to chassis ground. The purpose here is to avoid stray ground-loop radiation by minimizing inductive reactance between the device or cable ground and chassis ground. This minimizes impedance in the ground path. It is also important to keep the length of the unshielded conductor, near the connector, to a minimum.
When frequencies above about one kilohertz are used, ground path impedance can become a source of problems. These frequencies are common in most electrical equipment that employs radio circuitry or high speed switching circuitry. Thus, it is often necessary to create as nearly as possible a short-circuit ground path to the chassis for alternating currents. This is accomplished either by increasing ground conductor surface area or reducing path length. Grounding of shield wires in cable connectors may be accomplished by use of backshell type hardware, for braid pigtails which connect between braid shield and connector shell, or the pigtail may be inserted into a pin of the connector where it is carried through the mating connector and is grounded internal to the chassis to which the connector mates. The term pigtail is used to mean a wire that provides the electrical connection from a braid or shield to its termination point, but the term is not strictly limited to such wires Pigtails can also be formed of the braid itself where stripped from the cable. An example of backshell type hardware is shown in U.S. Pat. No. 4,111,513 to Thurston et al. Other grounding devices for pigtails and ground wires are shown, e.g., in U.S. Pat. Nos. 4,068,914; 4,906,199; and 3,513,433.
Cable termination devices, such as chassis-mounted connectors, require short terminations internal to the chassis. This is also true for other devices such as panel-mounted switches, fuse holders, and indicator lights. At present, the grounding hardware associated with the device can consist of a grounding stud such as a screw with a nut and washer installed at a location remote from the connector or similar device. Alternatively, backshell hardware can be employed, but that is somewhat expensive and is often difficult to install. Special pin and socket hardware is also available. None of these techniques serve the dual purpose of retaining the connector or other device and also supplying a nearby, convenient, low-impedance path to ground. Backshell hardware, while it can provide a short ground path, is expensive and heavy, and cannot be installed without special training. Also, rework and retrofit is difficult to implement. Special pin and socket hardware reduces path length, but adds space and weight to the finished connector assembly.